Bride standing to the left of the groom
This custom originated from our more savage past, when the wedding could be invaded by intruders at any moment.
Hence by positioning the bride on his left, the groom could hold her with his left arm and be ready to draw his sword at a moment’s notice with his right hand if need be.
In those days, brides were often ‘kidnapped’ from their families, so it could be her own family coming to get her back.